This invention relates to a polyurethane or polyurethane-polyisocyanurate foam prepared in the presence of a blowing agent which consists of an alicyclic and an aliphatic alkane.
It is well known to prepare cellular polyurethanes by reacting a polyisocyanate with an active hydrogen-containing material in the presence of a halocarbon blowing agent. In preparing flexible polyurethane foam, for example, halocarbons are often used to supplement water in generating a gas for blowing. However, the use of halocarbon blowing agents is particularly significant in making rigid foam. In rigid foam, the halocarbon blowing agent additionally provides thermal insulating properties and usually constitute the major proportion of the blowing agent when preparing a rigid foam. Of the halocarbons, trichlorofluoromethane (R-11), dichlorodifluoromethane (R-12) and trichlorotrifluoroethane (R-113) are of the most commercial importance; due to their advantageous thermal insulating properties, boiling points and stability. A disadvantage of these substances is that they are highly suspected of contributing to the depletion of atmospheric ozone. Accordingly, it would be highly desirable to replace the halocarbons with other blowing agents which are not believed to cause such environmental damage. Other blowing agents contemplated include hydrocarbons.
The general use of hydrocarbons including aliphatic and alicyclic alkanes as blowing agent when preparing polyurethane foam is known. U.S. Pat. No. 5,182,309 and European patent application EP-A-472,080 disclose the use of aliphatic alkanes including pentane as polyurethane blowing agent. U.S. Pat. No. 3,586,651 discloses the use of a cyclopentane/acetone mixture as blowing agent when preparing rigid, closed celled, polyurethane foam. Similarly in U.S. Pat. Nos. 5,096,933 and 5,034,424 the use of cyclopentane and/or cyclohexane in combination with other blowing agents to prepare polyurethane foam is disclosed. Combinations of halocarbons and hydrocarbons as polyurethane blowing agent are also disclosed in U.S. Pat. Nos. 5,132,332 and 5,001,164. Whilst use of hydrocarbons as blowing agent provides vis-a-vis ozone depletion a more environmentally acceptable system frequently, they do not permit the preparation of foam with long term commercially attractive physical properties including thermal insulation and dimensional stability characteristics.
Accordingly, it would be desirable to develop a process for the preparation of polyurethane foam in the presence of a halogen-free blowing agent and where the resulting foam exhibits long term thermal insulation and dimensional stability characteristics better suited to present commercial and environmental demands.